Page 309 - High Power Laser Handbook

278 So l i d - S t at e La s e r s Heat-Capacity Lasers 279

35
5 slabs
30

25 1.3
Output power (kW) 20 1.5 1.4 4 slabs 1.2 M = 1.1

Measured - 4 slabs
15

10

5 2
9.6 × 9.6 cm aperture
200 Hz - 10% duty cycle
Decade optical systems arrays
0
0.4 0.5 0.6 0.7 0.8 0.9
Output-coupler reflectivity
Figure 11.11 Output power as a function of output-coupler reflectivity and
slab count for a Nd:YAG heat-capacity laser.

11.3.2 The Effects of Amplified Spontaneous Emission
In a solid-state laser medium, a large fraction of the spontaneous
emission is trapped due to total internal reflection. To absorb this
radiation, and thus prevent internal parasitics from forming, edge
claddings are placed around the perimeter of the material, as shown
in Fig. 11.13.
The effect of ASE on stored energy may be modeled through an
artifice called the ASE multiplier, or M ASE . If no ASE were present in
the slab, the upper laser level would decay at the fluorescence decay
rate k = 1/t , where t is the fluorescence lifetime. In the presence of
F
F
F
ASE, the upper state will decay at rate k ASE = k M ASE − ) 1 , where
(
F
M ≥ 1. When M ASE = 1, no ASE is present. The ASE multiplier may
ase
be parameterized by the gain-width product, or the product of the
–1
gain coefficient (in cm ) with the width of the clear aperture (in cm)
of the slab.
We used a Monte Carlo three-dimensional ray tracing code to
8
calculate the ASE multiplier as a function of the gain-width product
for a given slab geometry. The code launches rays at random positions